1. Field of the Invention
This invention relates to a method of improving the insulating properties of high voltage electrical insulating devices and to the insulators manufactured thereby.
2. Description of the Prior Art
A persistant problem in the field of high voltage electrical insulating devices has been finding a suitable means for the prevention of leakage currents over the outer surface of the insulating devices. An early example of the problem and a solution is found in U.S. Pat. No. 2,428,608 to Bass in which an organopolysiloxane polymer was thickened and used as a grease to fill the space between an electrical conductor and a ground to prevent the formation of corona. U.S. Pat. No. 2,588,393 to Kauppi claimed a method of forming a film upon an article of manufacture comprising curing a mixture of methylhydrogensiloxane fluid and dimethylpolysiloxane high polymer on the surface to yield a tackfree surface. U.S. Pat. No. 3,511,698 to Talcott claims a process of applying to the surface of a rigid, cured thermosetting base member a dispersion of silicone elastomer stock and curing the same. In the examples, Talcott illustrated the improvement in arc resistance of an epoxy resin-glass fiber bar when it was coated with a 0.6 mm thickness of the silicone elastomer base. U.S. Pat. No. 4,011,168 to Uhlmann claims compositions of siloxane fluids, mineral filler, and a siloxane resin to produce grease-like compositions which are useful as electrical coatings to protect transmission insulators, distribution line insulators, and power substration bushings from flashovers.
The development of coatings for high voltage insulating devices such as suspension insulators and stand-off insulators used in electrical transmission and distribution systems has been necessary because the insulator, commonly constructed of glass or porcelain, becomes coated with contaminants which become conductive on exposure to moisture. Subsequent arcing over the surface may damage the insulator. The coatings disclosed in the prior art help to prevent this arcing by producing a hydrophobic surface to prevent the formation of continuous electrically conductive films on the insulator surface. The article "Self-Priming Silicone Elastomeric Coatings for High Voltage Insulator Bodies," Niemi, IEEE Conference Paper, 71C38 EI-25, 1971, disclosed a silicone elastomer that is useful for coating both ceramic type insulators and the new constructions of strong, lightweight synthetic or plastic insulators.